Means for producing an automatic warning signal



July 30, 1935. R. w. HART 2,009,447

MEANS FOR PRODUCING AN AUTOMATIC WARNING SIGNAL Filed May 29, 1931 4Sheets-Sheet 1 BY 97 ATTORNEY,

July 30, 1935. w HART 2,009,447

MEANS FOR PRODUCING AN AUTOMATIC WARNING SIGNAL Filed May 29, 1931 4Sheets-Sheet 2 v 97 4 i /00 9 96 54 53 lzllglvll III] I 95 f! 50 J o o O0 8] INVENTOR Roerf W Ham ATTORNEY July 30, 1935. R. w. HART 2,009,447

MEANSJ OR PRODUCING AN AUTOMATIC WARNING SIGNAL Filed May 29, 1951 4Sheets-Sheet 5 INVENTOR v Robe/'7 W Horf ATTORNEY July 30, 1935. R. w.HART MEANS FOR PRODUCING AN AUTOMATIC WARNING SIGNAL Filed May 29, 1931Band i We l l l l l l 4 Sheets-Sheet 4 INVENTOR Rqerf W Harf ATTORNEYIll:

Patented July 30, 1935 UNITED STATES PATENT OFFICE MEANS FOR PRODUCINGAN AUTOMATIC WARNING SIGNAL poration of Maine Application May 29, 1931,Serial No. 540,961

3 Claims.

The present invention relates to a system for receiving a warning signaland more particularly to such a system in which the warning signal istransmitted by electromagnetic waves to a ship or shore station.

Warning signals have in the past been commonly used. In wirelesscommunication at the present time the ship danger signal is given incode with the well-known letters S. 0. S. A ship in danger may broadcastthis signal and it is the duty of other ships in the vicinity to listento and receive the same and if possible lend assistance. Warning signalshave also been used for other purposes as, for instance, to make theposition of a ship known in time of fog.

In order to make use of these warning signals, since they aretransmitted at no special time, it is necessary constantly to have awireless operator on watch to receive the same. For continuous operationit practically becomes necessary under these circumstances to have atleast two operators upon a vessel which for a small crew is apt to be arather large expense.

In order to overcome this difliculty mechanical means have been adaptedand applied to give an automatic alarm when a proper warning signal istransmitted. Such alarms are in general operated in a number of ways.The signal may consist of a particular code arrangement to which onaccount of the mechanism in the receiving system the alarm at thereceiver will respond. In devices operated in this manner the warningsignal must be given quite accurately, and, further, the mechanismemployed for producing the selective operation for only the warningsignal is quite complex and expensive and easily gets out of order.

In my invention described below I overcome these and other objectionsand provide a simple, easily operated mechanism which is very rugged andwill not ordinarily get out of order. For a warning signal I prefer toemploy a long continued radio signal of a continuous or discontinuouswave source which is modulated by some low frequency wave. This type ofsignal has been employed for a warning signal and may comprise acontinuous or discontinuous radio frequency wave modulated by an audiofrequency tuning fork at, for instance, cycles. The signal may beoperated for a given period or for any period longer than the givenperiod, that is the radio frequency wave may have imposed upon it amodulation of 25 cyclesenduring for four or more seconds; The circuitwhich I-have devised is particularly adapted to receive this type ofsignal to the exclusion of all others.

A tuning fork which by continued operation over a given period of timebuilds up to a sufficient amplitude may be employed in the systcm forreceiving the type of the warning signal just described for the purposeof bringing about the operation of an alarm signal which .may be avisual indicator or a ringing device. While this type of apparatus hasproved to be very successful in alarm devices for the receipt of warningsignals of the type described above, the means employed in the presentinvention offers even greater reliability and freedom from interferingelements tending to create false signals and at the same time presents asystem in which the tuning element of the receiving circuit need not beextremely closely tuned to the tuning element of the transmittingcircuit.

In fact, even though the vibrating element in the receiving system isslightly out of tune with that in the transmitting device, the timeinterval in which the receiving system will operate may be keptextremely constant. Further, even though the amplitude of the vibratingelement in the receiving system is never very great, it is possible toprovide a consistent operation of the warning signal without anypossibility of false alarms.

In the system which I have devised for receiving warning signals of thistype I have separated in two different means the distinctive elements ofthe warning signal. A tuned vibratory system, mechanical or. electrical,may be used to pick up the tuned signal. If the tuned signal should thenendure for longer than a given period of time, the time-control meansconnected with the tuned means or circuit will operate and allow theoperation of the warning signal.

In the embodiment described in connection with this specification, amechanical vibratory relay is used tuned to the warning signal. Thisrelay, while tuned, does not need to be tuned so sharply as a tuningfork in the corresponding position. For making the operation of thealarm dependent upon the duration of the warning signal, there isprovided a thermionic valve circuit of the heater type in which theheating circuit is connected in the circuit of the tuned vibrator. Inorder for the thermionic valve to become operative, the cathode must beheated to a sufiicient degree by the heater which is accomplished onlyafter applying current for a given time. The vibrator intermittentlymakes and breaks the contact in the heater circuit of the tube and as aresult it takes a number of seconds for the tube to heat to the point ofoperation. ner if the warning signal has endured for the desired time,the circuit becomes operative and an alarm is sounded.

The separation of the time element and the tuning element is very usefuland important in the present system and by this means even though thetuned element at the receiving station should not be exactly tuned tothe modulated wave at the transmitting station, it would still bepossible to bring about a consistent operation of the warning signal. Insuch cases there is a possibility that the tuning fork 'or reed at thereceiving station may vary a small percentage in tuning and still notaffect the faithful operation of the system, since its operation of thesystem does not depend upon the building up of the amplitude of thevibrating member of the tuned system, but depends upon a separate andindependent element as will appear from the description in thespecification.

In the drawings Figure 1 shows a circuit arrangement of the receivingsystem, and Figure 2 shows a detail of the mechanically tuned vibrator,Figure 3 shows partly in section another view of the vibrator of Figure2, Figure 4 shows the transmitter modulating device and Figures 5 and 6show modifications of the receiver system.

In Figure 1 the signal, such as described above, is received in theradio frequency receiver and amplifier shown within the dashed lines Ifrom the antenna 2. The radio frequency receiving circuit has at leasttwo radio frequency tuners or amplifiers, the first of which, asindicated by 3, is tuned quite broadly to the radio frequency of thewarning signal to be received. This is, of course, the frequency of thecarrier wave and may in ordinary work be 300 or 600 meters. The secondradio frequency circuit 4 is tuned somewhat more sharply than the firstcircuit 3 and to a slightly different frequency than that of the firstcircuit. The first circuit 3 may be tuned, let us say, to 595 metersbroadly while the second circuit 4 may be tuned to 605 meters, but moresharply tuned. The radio frequency wave received and passed through thecircuits 3 and 4 is rectified in the usual manner in the detectorcircuit 5. If the signal happens to be a continuous wave signal, theoutput of the detector circuit may contain an audio frequency notemodulated at the pitch of the warning signal.

This would particularly be true where the carrier wave was heterodynedwith a local oscillator or where the heterodyned note was transmittedfrom the carrier station. The signal may, however, be merely the pitchof the warning signal. Ifthe transmitter was a discontinuous wave set,as, for instance, a. spark set, then the output of the detector circuitwould be, as has been previously described above, an audio frequencynote modulated at the pitch of the warning signal.

Either type of signal may be handled in the present circuit.

The detector circuit 5 impresses its output into an audio frequencyamplifier 6 which, in turn, operates the push-pull amplifier Icontrolling the warning signal operating circuit. To the output of thepush-pull amplifier I is connected the mechanical electrically drivenvibrator 8 which will be described in greater detail later. The vibrator8 is a tuned device being tuned by the tuned rod 9 which has anadjustable mass I0 positioned at its end. The vibrator is tuned to thepitch of the In this man-.

warning signal and responds within close range only to a signal of thatpitch or very closely to that pitch. If the vibrator in the present casewere turned to 25 cycles, it might respond somewhere from 24% cycles to25 cycles without great change in amplitude and would under suchcircumstances have sufllcient amplitude to alternately make and breakthe contacts I I and I2 operated thereby.

The contacts. and I2 are connected on the one side through the wire I3attached to the reed 9 to the heating element I4 in the thermionic valveI5. The contacts II and I2 on the other side are connected by means ofthe wire I6 to a contact I! on the alarm-ringing r'elay I8. Normally thecontact II is closed and the current passes through the relay stem IE!to the wire 20 connected to the cathode 2| of the tube I5 and to thecathode lead 22 to A- of the A battery. The lead 23 from the A+ connectsto the filament switch 24 and through this to the lead 25 to the heaterI4. It will be seen, therefore, that the closing of the contacts I I andI2 by the vibration of the mechanical vibrator 8 completes a circuitthrough the A battery and the heater I4 of the tube and commences theheating of the tube so that it may operate.

The alarm-ringing relay I8 has an operating coil 26 which, as will beseen from Figure 1, is connected through the lead 21 to the anode 28 ofthe tube I5. The operating coil 26 is connected at its other end to thelead 29 which connects to the positive potential of the power suppliedand returns therethrough by means of the leads 30 and 22 to the cathode2| of the thermionic valve I5. When the cathode 2| has been sufficientlyheated by the heater I4 through the intermittent operation of thevibrator 8, a current will fiow through the cathode-anode circuit of thetube including the coil 26 and will break the contact I1 and make acontact on the opposite side of the armature I9 with the contacts 3| and32. The contact made at 3| will energize the radio auto alarm 33 byconnecting the same across the A battery circuit as follows: leads 34,25, switch 24, lead 23, A battery, lead 36, lead 22, lead 20, armatureI9, contact 3| and lead 35. At the same time that the contact I'I isbroken and the thermionic tube I5 becomes inoperative because theheating current is broken, the contact 32 is made which completes thecircuit through the coil 26 across the power supply and maintains thecoil 26 energized so that the radio auto alarm will con tinue to ring.In order to stop the ringing of the alarm, the alarm release push button36 may be pressed which breaks this circuit and allows the armature I9to assume its normal operating position.

As the system must be operatively connected at all times, there isprovided a filament circuit alarm 31 operated by a filament circuitrelay 38 which is in series with the filament circuit supplying theheating current to the tubes of the radio frequency receiver. Theheating current is supplied to the tubes of the receiving set in aseries parallel connection, half of the tubes being connected in seriesand the two series circuits connected in parallel with the filamentleads.

If one filament should give way in this connection, the current throughthe filament relay immediately will be reduced to half its magnitude.The filament relay is so built that when this occurs the armature 33will no longer be attracted by the magnet and consequently be releasedand make a connection at 40 completing the filament circuit alarm acrossthe A battery. If any one of the filaments should burn up while thesetis being continuously operatedor in continuous operative condition, afilament circuit alarm will be given so that the operator may replacethe useless tube.

The entire receiving circuit may be tied up with the filament circuitalarm in this fashion, and, as indicated in Figure l, the audiofrequency amplifiers may similarly be connected in the filament circuitalarm.

In order to insure further continuous operation of the set, a B batteryis provided, as indicated in Figure 1, but normally this battery is notconnected in circuit, the power leads 29 and 30 being supplied directlyfrom the 110 volt D. C. mains. If for any reason the power supply shouldbe broken, the differential relay 4| across the mains will release therelay armature 42 and conmeet from the left contact 43 connecting to thepower mains to the right contact 44 connecting to the positive potentialof the B battery. At the same time, the battery charging no voltage,release relay 45 would also release and prevent the A battery which isnormally in charging condition through the lead 46 and the contact 41connecting the positive A potential to the positive side of the mainsfrom discharging through the power supply.

To provide further for faithful operation without the presence of falseor stray signals which might under very rare conditions be obtained by acontinuous discharge of very powerful static for a period of fiveseconds, there may be provided in the detector circuit, as shown at 5 inFigure 1, a resistance 200 connected in series in the heater leads and asecond resistance 20! connected across the heater element of thedetector tube. While these resistances may be permanent- 1y adjusted, itmay be preferable to provide an adjustable contact element shown by thelead 202 which has one connection 203 adjustably associated with theresistance 200 and another connection 204 adjustably associated with theresistance 20!.

In this manner the detector tube may have its cathode run at a lowtemperature, thereby limiting the strength of the signal current whichcould fiow through the circuit and at the same time providing maximumsensitivity. In this manner a powerful signal would be cut down while afeeble signal would be amplified in the usual manner.

It may also be preferable to provide a space current'meter, as shown by205 in Figure l, in the common cathode return lead. This space currentshould not fall below a given value, and if it does fall below a givenvalue, the operator knows that the circuit is not functioning properly.

Figure 2 shows the mechanical vibrating device and comprises the twocoils 48 and 49 with the poles 50 and 5|. The magnetic circuit throughthe coils is completed by the plate 52 at the bottom of the coils. otedby a center spring 54 and is alternately attracted by the poles 50 and5|, thus vibrating the rod 9 carrying the contacts I l and I2. Anadjustable weight 55 is provided for tuning the device to the desiredfrequency. Adjustment may also be obtained by means of adjusting screws56 and 51 by means of which contacts may be made with the contacts H andI2 at the desired amplitude of the mechanical vibrator. The devicedescribed may be sharply tuned and prefer or by both means.

contact H mounted on the screw 12 which may The armature 53 is pivablyin the present case is tuned within one or two cycles.

Figure 4 shows a means of modulating the transmitter at the desiredfrequency. It has been found that a tuning fork alone is not a goodmethod of modulating or making and breaking the carrier current. This isprobably due to the fact that the contacts are made and broken at theinstant when the velocity of the contacts with respect to one another isvery small and an arc tends to form for this reason. The system shown inFigure 4 has the advantage of preserving the correct frequency in theuse of the tuned rod or spring relay 60 and the power relay 6|.

The tuned relay 60 is operated across the line through a resistance 62and contacts I0 and H. This tuned device comprises a U-shapedelectromagnet 63 having two poles G4 and 65 and an armature 66 in theform of a strip of flexible iron or steel secured at one end toa block6'! and having at its other end a mass 68 from which a spring element 69extends carrying the con- .tact 10.

The armature may be tuned by adjustment of the mass 68 or by thinningthe metal at "H' Opposite the contact 10 is a be adjustably positionedin the block 13. Across the contacts-l0 and H is the condenser 14.

When current is applied on the electromagnet 63, the contacts 10 and IIare opened and closed at a period corresponding to the tuning of theelement 66. This likewise opens and closes the current through the coil15 of the relay 6!. The relay 6! may be any of the ordinary types ofquick acting relay but preferably is one in which the spring member 16furnishing the movement of the contact arm 11 is very strong and the armH itself is long. The contacts 18 and 19 are mounted at the end of thearm and fly back with a great velocity when the coil current is bro-ken.The relay may be made to have this quick action by having the spring 16of spring steel and very short and providing the contact arm 11 as alever to obtain a higher velocity at the contact points.

The relay contacts 18 and 19 may be in the circuit of the transmitterhaving a continuous current high frequency generator 8| of any of thewell-known types radiating electromagnetic waves through the antenna 82.

In place of using a wholly mechanical tuned system, a systemelectrically tuned may be used. This is shown in Figure 5 where theantenna 83 picks up the radio frequency signal which is received in thereceiving circuit 84 comprising a radio frequency amplifier 85, detector86 and audio frequency amplifier 81. The audio frequency amplifier 81 isconnected across a band pass filter 88 passing a small band in theneighborhood of 25 cycles or the frequency it is desired to pass.

The output 89 of the filter is connected across a thyratron or grid glowtube 9| capable of handling more power than the receiving circuit. Theoutput of this tube is heterodyned with a local oscillator 92 which maybe a dynatron generator 93 with a push-pull amplifier 94 or any othersuitable generator circuit or means. The heterodyne is designed toproduce a very slow beat note and this note is impressed by means of thetransformer 95 or any suitable means as a resistor, for example, uponthe no current relay device 96.

'I'he tube 91 in this element has its grid biased to cut off the currentflowing through .the plate circuit of the tube when the voltagedeveloped across the transformer 95 was zero because of the beat, beingreduced to nearv zero. That is when the beat note is near zero, thecurrent becomes almost zero value during some part of the beat cycle andat this moment the voltage generated by the transformer is zero. Whenthis occurs the inertia weighted relay 98 which operates only near zerobeat because of its design, is released and the alarm I00 operates.

In place of the circuit of Figure 5, the circuit shown in Figure 6 maybe used. Here the signal is received on the antenna 83 passed through areceiver circuit 84 and a band pass filter IM to obtain the particularwarning signal note. The band pass filter works into a power oramplifying means I02 which may be a tube circuit as shown and operates asolenoid relay I03, the plunger I04 of which is delayed by the dash potdevice I05 in which the plunger I06 is attached to a rocker link I01pivoted at I08. The rocker arm at the end opposite the plunger I06 ispivoted to the solenoid at I09. When the solenoid is pulled downward, asit is by the action of the 25 cycle current, the contact H0 is madeclosing the alarm circuit III.

It should also have been noted that the alarm tube heater I4 is providedwith a safety device comprising a high resistance relay I20 connected inthe heater circuit across the battery and the heater through whichsufiicient current flows at all times while the tube is in operation tomaintain the contacts I2I and I22 open at all times. If the heater I4should burn out, the current through the high resistance relay is brokenand contact is made between I2 I and I22 operating the alarm 31 andnotifying the operator that the device is not functioning properly.

Having now described my invention I claim:

1. In a wireless receiving system for receiving a warning signal havinga definite periodic interruption and of a definite length, a mechanicaltuned relay connected to the output of said receiving system, a valvehaving cathode and anode electrodes, means intermittently heating saidcathode by the operation of said relay, said means being commensuratedto produce a space current after the intermittent heating has continuedsubstantially for the signal length and means operated when the spacecurrent has been established.

. 2. In a wireless receiving system for receiving a warning signalhaving a definite periodic interruption and of a definite length, amechanical tuned relay connected to the output of said receiving system,a valve having cathode and anode electrodes, means intermittentlyheating said cathode by the operation of said relay, said means beingcommensurated to produce a space current after the intermittent heatinghas continued substantially for the signal length, means operated whenthe space current has been established and means for manually restoringsaid last means to its preoperative condition.

3. In a wireless receiving system for receiving a warning signal, avalve and valve circuit having cathode and anode electrodes, means forintermittently supplying heat to said cathode to accumulate sufiicientheat intensity to produce an electron flow after a definite period ofinter- 35 mittent heat supply and means operated by said

